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Diagnostic Procedures

  1. Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. After performing diagnostic system check, go to next step.
  2. Is there a DTC P0505 set? If yes, see DTC P0505 under DIAGNOSTIC TESTS in appropriate SELF-DIAGNOSTICS article. If no, go to next step.
  3. Start the engine. Run the engine until a normal operating temperature of at least 174°F (80°C) is achieved. Allow the engine to idle for at least 15 minutes after reaching operating temperatures. Operate the engine at 2500 RPM for 90 seconds. Release the throttle and wait 30 seconds while the engine idle stabilizes. Observe the Engine Speed and the IAC Motor Command parameters on the scan tool with the transmission in Park or Neutral. Are the Engine Speed and the IAC Motor Command within 650-750 RPM A/T or 650-750 RPM M/T, or 27-43 percent IAC Motor Command? If yes, go to step  5 . If no, go to next step.
  4. Operate the engine at a normal operating temperature. Select RPM Control, under IAC System, in the Special Functions menu of the scan tool. Command the IAC valve to increase and decrease the engine speed with the scan tool. Did the engine speed increase and decrease as commanded by the scan tool? If yes, go to next step. If no, go to step  8 .
  5. Start the engine. Place the transmission in Park or Neutral. Operate the following accessories, one at a time, while observing the Engine Speed and the IAC Motor Command parameters on the scan tool:
    • Turn ON the headlights.
    • Turn ON the rear window defogger, if equipped.

    Did the IAC Motor Command increase within 1-3 percent of IAC Motor Command? If yes, go to next step. If no, see ELECTRICAL/ACCESSORY LOAD IDLE-UP SIGNAL DIAGNOSIS  .

  6. Turn ON the HVAC blower motor and the air conditioning, if equipped. Did the IAC Motor Command increase within 4-14 percent of IAC Motor Command? If yes, go to next step. If no, see ELECTRICAL/ACCESSORY LOAD IDLE-UP SIGNAL DIAGNOSIS  .
  7. Turn OFF all accessories. Turn the steering wheel to the right and to the left. Return the steering wheel to the center, straight ahead position. Did the IAC Motor Command increase within 2-10 percent of IAC Motor Command, when the steering wheel was turned all the way in either direction? If yes, go to step  16 . If no, see ELECTRICAL/ACCESSORY LOAD IDLE-UP SIGNAL DIAGNOSIS  .
  8. Turn OFF the ignition. Disconnect the IAC valve electrical connector. Turn ON the ignition, with the engine OFF. Using a test lamp connected to ground, probe terminal No. 2 of the IAC valve connector on the harness side. See Figure . Does the test lamp illuminate? If yes, go to next step. If no, go to step  12 .
  9. Using a test lamp connected to battery voltage, probe terminal No. 3 of the IAC valve connector. Does the test lamp illuminate? If yes, go to next step. If no, go to step  13 .
  10. Turn OFF the ignition. Jump terminal No. 2 of the IAC valve connector on the harness side to terminal No. 2 of the IAC valve connector with a fused jumper wire. Jump terminal No. 3 of the IAC valve connector on the harness side to terminal No. 3 of the IAC valve connector with a fused jumper wire. Connect a fused jumper wire to terminal No. 1 of the IAC valve (not the harness). Insulate the terminal No. 1 jumper from contact to ground. Start and idle the engine. With the engine idling, repeatedly touch the terminal No. 1 jumper to battery ground with a rapid ON-OFF motion. Does engine speed increase as the terminal No. 1 jumper is rapidly grounded ON and OFF? If yes, go to next step. If no, go to step  14 .
  11. Turn OFF the ignition. Remove all jumpers. Disconnect the PCM connector containing the IAC valve open control circuit. Check terminal No. 1 of the IAC valve open control circuit for a grounded, open, or shorted to voltage circuit. Repair the circuit as necessary. Was a circuit repair made? If yes, go to step  16 . If no, go to step  15 .
  12. Locate the cause of no power to the IAC valve connector. Repair as necessary. After repairs, go to step  16 .
  13. Repair the open IAC valve ground circuit. After repairs, go to step  16 .
    14. NOTE: The IAC valve seals the coolant passage of the throttle body
  14. Replace the IAC valve. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repairs, go to step  16 .
  15. Replace PCM. Perform PCM relearn procedure. See POWERTRAIN CONTROL MODULE under PROGRAMMING in appropriate SELF-DIAGNOSTICS article. After replacing PCM, go to next step.
  16. Turn OFF all accessories. Ensure that the engine is operating at a normal temperature. Observe the Engine Speed and the IAC Motor Command parameters on the scan tool with the transmission in Park or Neutral. Are the Engine Speed and the IAC Motor Command within 650-750 RPM A/T or 650-750 RPM M/T, or 27-43 percent IAC Motor Command? If yes, go to next step. If no, see ROUGH, UNSTABLE OR INCORRECT IDLE & STALLING in appropriate TROUBLE SHOOTING - NO CODES article.
  17. Operate the vehicle within the conditions in which the customer concern was first noticed. Is the concern still present? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS in appropriate SELF-DIAGNOSTICS. If no, system is okay.
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